I have setup with a Cerbo gx, 2 MPPTs, an Orion XS, a smartshunt a Creabest Charger/Inverter and Lead-acid batteries for both starter and aux.
I need to replace the aux battery and would like to go for the Victron 300Ah NG lifepo4.
But…
I need a BMS and can’t figure out what would be the best way to go. At first glance I would say the VE.Bus BMS NG, but I don’t have a multiplus, therefore nothing to connect the BMS to, right? Would I have to connect it to the Cerbo? If so, what would be the benefit/effect/use?
I understand the BMS can never tell the charger/inverter to shutdown, but what about the MPPTs and Orion?
Different option would be the SmallBMS NG with no VE.Bus at all. So there will be no communicaton at all. Is there any direct danger in the fact that the BMS can;t control load or chargers?
The small BMS NG has to have the ATC and ATD (Allow to Charge / Discharge) terminals connected to the remote on/off terminals of the chargers and loads to shut them down as long as they support this, otherwise the ATC connects to a Smart Battery Protect. To shut down loads from the ATD terminal use a Smart Battery Protect ( not the same one as on charging sources) in lithium mode. Details in the manual.
The VE Bus BMS NG receives negative connection to the battery via the inverter VE bus cable. There is a hack to power it directly without a VE Bus device, see link at the bottom of this post. With the Cerbo GX connected, the VE Bus BMS will shut down chargers using DVCC if the charger is connected to the Cerbo and supports DVCC control. Unsupported chargers will need the ATC terminal connecting to a Smart Battery Protect. For load shutdown you would still need the ATD terminal connecting to a Smart Battery Protect.
There is a VE CAN BMS in development, which is the same as the VE BUS BMS but connects to the Cerbo via VE CAN and does not need an inverter in the system. That is probably a 2027 product though.
Okay, so this is way more complicated than I thought…
My charger/inverter has no way to remotely shut it off (not that I know of, anyway) and is both charger and load, so I can’t put a smart battery protect in there (even if it could handle the current). That would be a problem that I wouldn’t know how to solve.
Then, I would hope that my other chargers, that are DVCC controlled, would not need any new connections, if the BMS is talking to the Cerbo. So will the VE.BUS BMS talk to the Cerbo over VE.BUS for this?
If I go the SmallBMS route, it will not talk to the Cerbo at all, so I would need to connect every single charging device to the ATC…not really an option I like.
As far as disconnecting other loads, I would need a smart battery protect connected to the ATD of the BMS, but these other loads can not include MPPTs, Orion, cerbo etc? Otherwise my system would shut down completely…
You can never really remove all loads anyway, so is there really a point in installing a battery protect for small things that are not drawing power by default (like lights, water pump etc)?
People also use LiFePO4s with built in BMSes that don’t communicate with Victron at all…how do they manage ATD and ATC?
3rd party batteries with a built in BMS and no communication have solid state switches (FETS) between the cells and yhe battery terminals. If the cells are too hot, too cold low voltage or high voltage the BMS just isolates the cells from the terminals to keep the cells safe. What the rest of the system does depends on many things, solar may keep it alive in daylight hours, if you were charhing at high current a BMS disconnect may result in a voltage spike damaging your equipment.
If your inverter has no remote on/off then you can look into a contactor as produced by companies like Tyco, but you may need a solid state relay between the BMS ATC and ATD and the contactor like the Victron SolidSwitch 104 if the ATC/ATD do not have enough current capability for a contactor.
If you have loads on the system, even small ones these can drain a lithium battery so far that it is damaged even after the main loads have been isolated. The other option is to have a single contactor between the batteries and the whole system. This is what the Lynx BMS does, DVCC controls everything, a SBP stops loads that can be stopped and in extremis, the contactor opens.
The VE BUS BMS does talk to the cerbo to stop charging DVCC controlled chargers like SmartSolar and Orion.
But there is the catch22 in my opinion… If I have a battery protect disconnect all loads from the batteries, there is very little it can disconnect: the cerbo needs to stay operational to run DVCC, the MPPTs need to stay operational in order to be told to stop charging, etc, etc. The battery protect can never shut itself down. The BMS also needs power.
So although, in theory, you should disconnect all loads to protect your battery, in practice you can never really do this, right?
The system is such that for loads to be turned on by a SBP, the BMS has to generate a +12V signal, if the BMS is shutdown then it can not do this, so the SBP will shutdown the loads. Typically a system will not reset until you get a 12V supply connected to the system. Reading the manuals and wiring schematics in detail will answer many questions.
@Franc As you seem to be after a simpler system with the added issue of a non controllable inverter/ charger have a look at the Victron Superpack NG batteries. These have built in BMS but no detailed communications. I have no experience with these as I am using the NB batteries and Lynx BMS with Multiplus inverter/ charger.
Something that I never really looked into, but might help: the inverter has a setting to shut down the inverter if the voltage drops below a set value
Coud this help in making the setup safer if a BMS can’t stop the inverter?
Also, I can configure the charger for Lithium batteries (specific bulk an float voltages), so it will charge the battery correctly, but of course will not stop charging in the event of…
Only if the BMS isolates the DC to the inverter which will be the case with a battery with built in BMS or if you add a contactor triggered by ATC/ ATD from the small or VE Bus BMS. It also depends on the Orion and MPPT charging being stopped as these could keep the voltage high enough until you got a high current drawn from the ac side.